It is known to provide marine vessels with roll stabilizers in the form of fins which extend in a non-vertical orientation, the roll stabilizers being controllably rotatable so as to generate hydrodynamic forces perpendicular to the direction of travel as the vessel moves through the water. The roll stabilizers are controlled so that the forces act in the direction opposite to the direction in which the vessel is rolling and as a consequence serve to stabilize the vessel by counteracting the roll.
Roll stabilizing forces are commonly generated either by rotating an entire fin or by providing a fixed fin portion and a flap portion rotatable relative to the fixed fin portion.
However, since roll stabilizers are required to be always disposed in the water, the roll stabilizers are difficult to access for maintenance, and hitherto it has generally been necessary to remove the ship from the water by slipping or dry docking in order to access the roll stabilizers. Facilities for dry docking relatively large marine vessels are scarce, and dry docking a marine vessel is relatively time consuming and expensive.
For relatively large marine vessels, relatively large and heavy roll stabilizers are required and as a consequence it is impractical to employ underwater divers to carry out maintenance of the roll stabilizers with the vessel afloat. In addition, roll stabilizers can generally not be removed from a marine vessel while the marine vessel is afloat because removal of a roll stabilizer would breach the watertight integrity of the vessel.
Moreover, roll stabilizers known hitherto often include a hinged connection between the rotatable flap portion and the fixed fin portion, thus making maintenance on the hinge bearings extremely difficult.